1. Field of the Invention
This invention relates to a circuit interrupting switch for use at relatively high voltages and, more particularly, to control circuitry for an operator for opening and closing the contacts of such a switch wherein the switch is normally prearmed in a pre-close or pre-open position to reduce the time period between a switch command and operation of the switch contacts.
2. Description of the Prior Art
Circuit interrupting switches are generally old and well known in the art. An example of such a switch is disclosed in U.S. Pat. No. 3,947,650, assigned to the assignee of the present invention. Such switches utilize a snap-action mechanism, such as the snap-action mechanism disclosed in U.S. Pat. No. 3,908,473, for opening and closing the switch contacts. The snap-action mechanism, which includes a spring, is not used to store energy in a non-active state. When a switch operation is desired, a lever arm, disposed outside the switch housing, is used to transfer energy to the snap-action mechanism. Once sufficient energy has been transferred to the spring, continued motion of the lever will release a mechanical latch. Release of the latch allows the spring to open or close the switch contacts.
The total time for the switch to operate in response to a command is comprised of two time periods; namely, the charging or prearming time and the switch contact operation time. The prearming time is the time it takes to transfer sufficient energy to the spring in the snap-action mechanism to cause the switch contacts to open or close. The charging or prearming time does not influence the switch contact operation time. This prearming time is controlled by the speed of travel of the lever arm which may be either manually operated or motor operated. The switch contact operation time is the time it takes the switch contacts to operate after the latch has been released. This time period is relatively small as compared to the prearming time.
FIG. 1 is a one line diagram of a pair of circuit interrupting switches used to feed a critical load. With such an arrangement, the configuration of the circuit interrupting switches would be such that one switch would be closed and the other switch opened at one time. This would allow a preferred source of electrical power to be connected to the critical load during normal operation. However, if the preferred source becomes unavailable, the configuration of the circuit interrupting switches is reversed so as to connect the alternate source and disconnect the preferred source from the critical load. With conventional circuit interrupting switches, typical motor operations would take approximately six seconds (three seconds for each switch). However, there are certain applications where six seconds would be unacceptable, such as lighting systems used for night sports events, and the like. For such applications, in order to solve this problem, the equipment would have to be replaced with interrupting devices with stored energy mechanisms. Such equipment replacement is relatively expensive.